The opening edge structures of the tank parts of the water tank known from EP 0870877 B1 and from the brochure “Systematic Rainwater Use”, page 34, edition 2006, of the company Otto Graf GmbH Plastic Products, D-9331, Teningen, Carl-Zeiss-Str. 2-6, catalogue R26, are designed such that the outer flattened opening edge only has a width corresponding to the thickness of the sealing channel wall, and the inner opening edge has a width corresponding to the thickness of the tank part wall. The water tank is manufactured from two cup-shaped, identical halves by local clamping joining of the opening edge structures with clamp-shaped quick connectors. When both halves are joined and clamped together, the outer opening edges contact each other, while the inner opening edges are distant from each other. A unitary sealing strip is contained in the sealing channels of both halves. The sealing strip has a double conical cross-section. The quick connectors are pushed at the outer side along the circumference of the water tank over the clamp skewbacks. The quick connectors and the sealing strip contribute significantly to the cost of the water tank. The plastic material e.g. is HDPE or PP, in particular glass fibre reinforced PP. The water tank can only be assembled with the quick connectors in separable form. This joining principle is of advantage when the halves have to be transported for long distances to the site or into foreign countries, because the halves are stacked during transport for logistic reasons, require, however, a relatively complicated assembly on site. Manipulating the heavy halves during the assembly with a the weight of one half of e.g. 30 kg, threading the sealing strip and mounting the e.g. 24 quick connectors is time-consuming and means a significant cost factor which might negatively influence the acceptance at the site of some end users. In case of shorter transport distances or favourable transport conditions e.g. inland, the cost factor of the assembly on site may become much more important than the cost advantage of a stacked transport. This means that then the assembly of the water tank already at the producer's site or at the distributor and the delivery of the assembled water tank would be more favourable and more acceptable to more end users. In such cases it would be desirable to deliver the water tank ready for installation, however, without quick connectors and the sealing strip, e.g. by welding the halves to each other without quick connectors and without a sealing strip. However, the narrow opening edges of the halves of the known water tank do not allow reliable and watertight welding.
DE 9416968 U discloses an exclusively separable version of a water tank which is joined from two tank parts which are not identical among each other. The tank parts are deep drawn from fibre reinforced plastic material. The releasable clamping connections of the tank parts are local screwed connections along the opening edge structures of both tank parts. The tank parts are screwed together with the sealing means inserted into the sealing channels to make the water tank watertight. Inclined alternating flange portions at the outer side of the outer fitting surfaces protrude downwards and upwards beyond the joining plane to facilitate centering the tank parts prior to the joining process. The inclined flange portions increase the stiffness of the opening edge structures. Ribs formed in the tank part walls terminate with a distance from the joining plane at a circumferentially continuous apron. The tank parts either are joined at the manufacturer's site or on site.
DE 19909041 A discloses a multi-chamber plastic material container assembled from two injection moulded container parts which are not identical among each other and which have wide fitting surfaces in the joining plane which fitting surfaces are wider than the wall thickness. The container is intended to be mounted in automobiles. The fitting surfaces are surface-fused and pressed against each other when joining the container parts by welding. The container typically is used to store operating liquids like a brake liquid or windshield cleaning liquids.